The invention relates generally to x-ray tubes, and more particularly to a casing for enclosing the various components of the x-ray tube insert.
X-ray systems may include an x-ray tube, a detector, and a support structure for the x-ray tube and the detector. In operation, an imaging table, on which an object is positioned, may be located between the x-ray tube and the detector. The x-ray tube typically emits radiation, such as x-rays, toward the object. The radiation passes through the object on the imaging table and impinges on the detector. As radiation passes through the object, internal structures of the object cause spatial variances in the radiation received at the detector. The detector then sends data received, and the system translates the radiation variances into an image, which may be used to evaluate the internal structure of the object. The object may include, but is not limited to, a patient in a medical imaging procedure and an inanimate object as in, for instance, a package in an x-ray scanner or computed tomography (CT) package scanner.
The X-ray tube includes an x-ray tube insert and an x-ray tube casing. The x-ray tube insert is the functional device that generates x-rays, while the x-ray tube casing is a housing that surrounds, protects and supports the insert. The x-ray tube casing performs the following functions:                physically supporting the x-ray tube insert inside the x-ray tube casing so that an x-ray transmissive window on the x-ray tube insert is held in a position registered to the x-ray transmissive window in the x-ray tube casing, enabling x-rays produced within the x-ray tube insert to exit the x-ray tube assembly and illuminate the object of interest;        shielding of x-rays emanating from the x-ray tube insert except for a defined portion that pass through x-ray transmissive window(s) toward the object of interest;        supporting the motor stator relative to the motor rotor for a rotating anode x-ray tube;        providing for high-voltage electrical connections between the x-ray tube insert and the high voltage generator, which are typically made via high voltage plug and socket or via a high voltage connector being removably secured to a high voltage insulator with a silicone gasket in-between;        hermetically enclosing and directing a coolant within the x-ray tube casing around the x-ray tube insert—the vacuum vessel of the x-ray tube insert gets very hot when operated and that heat is removed by circulating a dielectric coolant over the x-ray tube insert vacuum vessel that is subsequently pumped to an external heat exchanger where the heat is rejected to the room air or to another liquid coolant before being returned to the x-ray tube casing; and        operably connecting the x-ray tube insert to the imaging system gantry or positioner.        
Looking at FIGS. 1-2, a portion of a typical medical x-ray tube casing 10′ includes an aluminum housing 12′ with a lead (Pb) shielding sheet 14′ pressed into and against the interior surface or wall 16′ of the aluminum housing 12′, except over a transmissive window 15′ secured over an opening in the housing 12′. The lead sheet 14′ is typically bonded with an epoxy to the interior wall 16′ of the aluminum housing 12′. The interior surface 18′ of the lead sheet 14′ is also painted to prevent oxidation and contamination of the dielectric coolant 26′ that comes into contact with the interior surface 18′ of the lead sheet 14′.
The aluminum housing 12′ is typically fabricated by a casting technique, machined from bulk material, or fabricated from separate formed pieces that are joined together by welding and/or brazing processes. For manufacturing and economic reasons a constant thickness lead sheet 14′ is pressed into the housing 12′. The lead sheet 14′ lining process is laborious as it is important that there are no gaps between the housing 12′ and the sheet 14′ where unwanted radiation can escape from the casing 10′. This is particularly challenging at joint transitions between parts of the housing 12′. Consequently, uniform thickness shielding is present across the entire interior surface 16′ of the housing 12′, resulting in more lead 14′ being employed than is required, particularly in areas of the housing 12′ where stray x-ray emission is low. This is negative for a number of reasons:                increased material and manufacturing costs for the assembly of the casing 10′ using the excess lead sheet 14′;        the handling and installation of the x-ray tube casing 10′ is difficult due to the increased weight of the casing 10′, normally requiring more than one person or mechanical assists; and        the structure of the gantry or positioner of the medical imaging system must be more substantial to handle the increased weight of the casing 10′ which increases the cost of the system.        
Looking now at FIGS. 3-4, the x-ray tube casing 10′, such as that commonly used on interventional imaging systems is illustrated including two high voltage receptacles 22′ attached to opposed end caps 21′ connected to a center frame 23′ of the aluminum casing 10′ that are each operably connected to a high voltage generator (not shown). The casing 10′ additionally includes a heat transfer circuit 25′ utilizing a cooling system disposed externally of the tube 10′ and including a water chiller 27′ and pump 29′ circulating cooled water through a dedicated tube coolant to water heat exchanger 24′ to thermally contact and cool the dielectric tube coolant 26′ contained within the casing 10′ and pumped through the opposing side of the heat exchanger 24. The tube coolant 26′ passes through a filter 28′ that preserves the electrically insulating properties of the dielectric coolant 26′. As schematically shown in FIG. 4, the coolant 26′ is present within the casing 10′ to support the x-ray tube insert 30′ within the casing 10′ as an intermediate layer to provide heat removal from the insert 30′.
For a high power interventional x-ray tube insert 30′, for the x-ray casing 10′ a typical wall thickness of aluminum housing 12′ is several mm and the lead sheet 14′ is approximately two (2) to four (4) mm thick. The dimensional tolerance on the thickness of the lead sheet 14′ is usually relatively large owing to the lower precision manufacturing processes used to place the lead sheet 14′ into the housing 12′ for the casing 10′ and the need to maintain a minimum thickness for sufficient radiation shielding. Due to the wide tolerance of the lead sheet 14′, a typical coolant gap in a conventional tube casing is held from about 2.5 to 3.5 mm.
While sufficient to cool the tube coolant 26′ from within the casing 10′, the dedicated tube coolant-water heat exchanger 24′ and associated cooling circuit 25′ creates added cost and weight and size to the x-ray tube casing 10′, in addition to that created by the lead sheet 14′. Further, the size of the tube casing 10′, including the heat exchanger 24′/cooling circuit 25′ mounted to the exterior of the casing 10′, limits the degree of oblique imaging angles around the patient and can compromise the quality of exam performed.
As a result, it is desirable to develop a structure, method of manufacture and method for use of an improved x-ray tube casing that is designed to reduce the weight and size of the casing while improving the cooling capacity and x-ray shielding capabilities of the casing when in use.